This invention relates to a method for manufacturing polarized spectacle lenses having a high polarization coefficient.
Polarizing lenses made of glass have been manufactured for a long time. A glass polarized lens is formed by placing a polarizing film and a bonding agent between two glass lenses and pressing them together. Recently, in order to light-weight spectacle lenses and to avoid damages to eyes by broken lenses, lenses have been made of plastic materials.
Examples of methods for manufacturing plastic lenses are as follows.
(1) A casting method as disclosed in, for example, Japanese Patent Application Publication No. SHO 47-35050 A, according to which method a polarizing film preformed to have a spherical surface is placed in a cavity formed by molds having concave and convex inner surfaces, and a polymerizable plastic monomer, e.g. diethylene glycol biscarbonate, is injected on opposite sides of the polarizing film and polymerized.
(2) A press molding method as disclosed in Japanese Patent Publication No. SHO 50-3656 B, according to which thermoplastic sheets having different thicknesses are placed on opposite sides of a polarizing film and compressed.
(3) A method as disclosed in Japanese Patent Application Publication No. SHO 56-13139 A, according to which a polarized plastic lens is fabricated by the use of a polarizing sheet formed of a polarizer directly bonded to a fusible material.
(4) A method as disclosed in Japanese Patent Application Publication No. SHO 64-22538, according to which a polarized polycarbonate lens is fabricated by stacking a polarizing film and polycarbonate films or sheets with the polarizing film disposed between the polycarbonate films to thereby provide a laminate having a thickness of 0.5-2.5 mm, and the laminate is hot-molded under pressure.
These methods, however, have disadvantages. For example, they require a long manufacturing time; the polarizing sheets are of special structure and, therefore, expensive; deformation may be introduced when sheets are subjected to thermal formation; and manufacturing lenses of different colors requires a corresponding number of colored polarizing sheets. Also, polarized lenses manufactured by the prior art methods are poor in impact resistance.
In order to overcome these problems, a method in which polyurethane resin is cast has been recently employed, but lenses manufactured by the casting method are expensive.
Many of optical lenses can hardly block selectively light in a wavelength region around 580 nanometers which makes human feel glare. Conventionally, in order to reduce glare, glass lenses have employed transition-metal compounds which are stable at a melting temperature of glass. Some types of plastic lens are formed of plastics, e.g. diethylene glycol biscarbonate, which can be injection-molded at a temperature of 100xc2x0 C. or below. Transition-metal oxides compatible with such injection-moldable plastics have a thermal decomposition temperature lower than the molding temperature of the plastics and, therefore, cannot be used for the purpose of glare reduction of plastic lenses.
An object of the present invention is to provide a method of economically manufacturing polarized spectacle lenses having high impact resistance and good optical characteristics. The method according to the present invention makes it possible to manufacture polarized spectacle lenses of various colors and light transmissivity using a single type of polarizing film.
The present invention can solve the above-described various problems by providing a new method for manufacturing polarized spectacle lenses. According to the invention, a polarizing film having a high light transmissivity and a polarization coefficient or degree of polarization extremely close to 100%, prepared by technologies used in making liquid display devices, which have made remarkable progress recently, is sandwiched between cellulose resin films to form a polarizing sheet. A plastic film, e.g. a polyurethane film, which is optically transparent and compatible and fusible with a plastic lens molding material, is placed on one surface of the polarizing sheet with an adhesive disposed between them. The resulting laminate is hot-pressed to have a surface contour conformable with the final shape of the lens, and the hot-pressed laminate is shaped, e.g. punched, into a shape conformable with the lens forming mold cavity. Then, the shaped laminate is placed in the cavity with the plastic film facing inward of the cavity. Thereafter, a plastic lens-molding material is injected into the cavity to complete the plastic polarized spectacle lens.
A polarizing sheet is formed by bonding, with an adhesive, a film of a cellulose resin selected from a group consisting of cellulose triacetate and cellulose acetate butyrate, on each of opposite surfaces of a polarizing film. The resulting polarizing sheet has a thickness of 0.2 mm or smaller, a light transmissivity of 40% or higher, and a polarization coefficient of 99.0% or higher. A plastic film having a thickness of from 0.1 mm to 0.5 mm and a light transmissivity of 80% or higher is stacked on and bonded to the polarizing sheet with an adhesive. The resulting stack or laminate is hot-pressed to have a surface contour similar to the surface contour of an ultimate lens. The hot-press shaped laminate is placed in a mold cavity with the plastic film facing inward, and a lens forming resin which can be fused with the plastic film is injected to complete the aimed polarized spectacle lens.
When polyurethane is used for the plastic film to be stacked on one surface of the polarizing film, it can be formed to have a thickness of from 0.1 mm to 0.5 mm. Further, when polyurethane resin is used as the lens molding material, a transition-metal compound can be mixed into the polyurethane resin.